1. Field of the Invention
The present invention relates generally to the decoding of convolutionally coded signals, and in particular, to a low-power, state-sequential Viterbi decoder for code division multiple access applications.
2. Description of the Related Art
In recent years, there has been a rapidly increasing demand for battery powered wireless communications. As this demand continues to increase, minimizing decoder power consumption becomes a critical concern.
Code-division multiple access (CDMA) modulation techniques have been widely applied in a variety of wireless communications products, including digital cellular telephones. CDMA is a convolutional coding technique that permits low power broadband transmission and reception of information with reduced interference, increased security, and adaptable channeling.
To support the large channel capacity required in digital cellphone network, a small E.sub.b /N.sub.o signal to noise ratio (SNR) per bit for a given bit error rate (BER) is needed. This requires that channel coding be performed with a relatively large constraint length convolutional code. Unfortunately, decoder computational complexity dramatically increases with convolutional code constraint length. At the same time, the demand for high bandwidth communications is increasing, even for mobile communications. High bandwidth transception requires decoding computations to be performed at extraordinarily high rates. Because of these channel capacity and bandwidth requirements CDMA decoding techniques are typically implemented in special purpose, very large-scale integrated (VLSI) circuits.
The power consumption, circuit size, and throughput of these special purpose VLSI decoders are major design concerns. Power consumption drives battery life, and extended battery life will be a prerequisite in future designs. Circuit size drives the size of the end-user product as well as throughput. It can therefore be seen that there is a need for a size and power efficient convolutional decoder. The present invention satisfies that need.